354 Limits of our Coal Supply. [July, 



working coal will be altered accordingly. In the cases 

 quoted by the Commissioners, the few degrees bf cooling 

 were effected by a system of ventilation that was devised to 

 meet the requirements of respiration, and not for the 

 purpose of cooling the mine. 



It would be very presumptuous for any one in 1873 to say 

 how this special cooling will actually be effected, but I will 

 nevertheless venture to indicate one or two principles which 

 may be applied to the solution of the problem. First of all, 

 it must be noted that very deep mines are usually dry; and 

 there is good reason to believe that, before reaching the 

 Commissioners' limit of 4000 feet, dry mining would be the 

 common, and at and below 4000 feet the universal, case. 

 At present we usually obtain coal from water-bearing strata, 

 and all our arrangements are governed by this very serious 

 contingency. With water removed, the whole system of 

 coal-mining may be revolutionised, and thus the aspect of this 

 problem of coolingthe workings would become totally changed. 



Those who are acquainted with the present practice of 

 mining are aware that when an estate is taken, and about to 

 be worked for coal, the first question to be decided is 

 the dip of the measures, in order that the sinking may 

 be made " on the deep " of the whole range. The pits 

 are not sunk at that part of the range where, at first sight, 

 the coal appears the most accessible, but, on the contrary, 

 at the deepest part. It is then carried on to some depth 

 below the coal seam which is to be worked in order to form 

 a "sumpf" or receptacle, from which the water .may be 

 wound or pumped. The necessity for this in water-bearing 

 strata is obvious enough. If the collier began at the 

 shallowest portion of his range, and attempted to proceed 

 downwards, he would be " drowned out " unless he worked 

 as a coal-diver rather than a coal-miner. By sinking in the 

 deep he works upwards, away from the water, which all 

 drains down to the sumpf. 



The modern practice is to sink " a pair of pits," both on 

 the deep, and within a short distance of each other. The 

 object of the second is ventilation. By contrivances, which 

 I need not here detail, the air is made to descend one of the 

 pits, " the downcast shaft," then to traverse the roads and 

 workings wherein ventilation is required, and return by a 

 reverse route to the " upcast shaft," by which it ascends to 

 the surface. 



Thus it will be seen that, whenever the temperature of 

 the roads and workings exceeds that of the outer atmo- 

 sphere, the air currents have to be forced to travel through 



